[Ashlandchris]

Interesting question. As a chemist I would say it doesn't matter as they are simply conveniently abbreviated names.
NiCad was the abbreviation for Nickel Cadmium ( which would have been Ni Cd if official chemical symbols had been used) and as was already said, LiPo stands for Lithium Polymer, so the chemical symbol for Lithium is Li, but as Polymer is not a single chemical, it is a compound of carbon / hydrogen / oxygen and other elements, it has no symbol.
Because they are "sort of" chemical names, the standard chemical naming process requires an abbreviation to either a single capital letter or a capital followed by a lowercase so NiCad and LiPo "sort of" look correct, but in actual fact neither are as there is no right and wrong (well, except NiCd)
Hope that helps?